Ground Loop (thing)

This is one of the main potential dangers of tail wheel aircraft. Tail wheel aircraft have the 2 main gear forward of the center of gravity (CG) and a small wheel located well aft of the CG. The CG will tend to try to lead the main gear. If the directional control of the aircraft is not maintained and the CG moves outside of the track of the 2 main gear, then the plane can begin to yaw and the wing that is on the outside of the rotation will dip and contact the ground. Imagine pushing a tricycle backward. It will start to turn one direction and tip over if you push it hard enough.

The problems that can occur include damage to the wing tip and the entire wing, depending on the severity of the ground loop. Also the gear box which supports the weight of the airplane can collapse as all of the weight of the airplane is loaded on a single gear box. The ground loop is the main reason that pilots need a tail wheel endorsement in their logbooks, to demonstrate that they know the reasons behind and avoidance of ground loops.